1. Field of the Invention
The present invention relates to a semiconductor device which has highly reliable electrode structure.
2. Discussion of Background
FIG. 1 is a sectional view showing a conventional semiconductor device having photoelectric conversion function, such as a solar cell of gallium arsenide (GaAs). As shown in FIG. 1, an n-type gaAs layer 2 and a p type GaAs layer 3 are laminated on the surface of an n-type GaAs substrate 1. A p-n junction 4 is defined between the n-type GaAs layer 2 and the p-type GaAs layer 3. Electrodes 5 are formed on both end portions and a central portion of the p-type GaAs layer 3, to be in ohmic contact with the p-type GaAs layer 3. A number of electrodes 5 are practically used and they may form a comb-type electrode. A p-type AlGaAs layer 6 is formed on a region of the p-type GaAs layer 3 provided with no such electrodes and an antireflection film is formed on the p-type AlGaAs layer 6. The antireflection film 7 is made of a nitride silicon film of 600 to 800 .ANG. in thickness.
Sunlight incident upon the antireflection film 7 is transmitted through the antireflection film and the p-type AlGaAs layer 6 and absorbed mainly in the p-type gaAs layer 3, to generate electron-hole pairs. Electrons, being minority carriers in the p-type gaAs layer 3, are diffused to reach and pass through the p-n junction 4 to thereby generate photoelectromotive voltage and photoelectromotive current, which are drawn out from the electrodes 5 and 8 so that radiant energy (electromagnetic energy) of the light is converted into electric power. This rate is generally called photoelectric conversion efficiency. In order to improve such photoelectric conversion efficiency, the p-type gaAs layer 3 must be minimized in thickness so that the p-n junction 4 is as close as possible to the light receiving surface.
A semiconductor device having photoelectric conversion function of this type may be used in space as a power source for an artificial satellite, and thickness of the layer 3 is preferably reduced in order to avoid damage by radiation. In general, such film thickness is about 0.5 .mu.m.
In the aforementioned conventional semiconductor device having photoelectrio conversion function, the electrodes 5 are directly formed on the p-type gaAs layer 3 in ohmic connection manner. Therefore, stress is extremely applied to the p-type GaAs layer 3, the n-type GaAs layer 2 and the p-n junction 4 taking important parts in photoelectric conversion, for connecting the electrodes 5 with external lead terminals (not shown) by a process such as welding or thermocompression bonding.
Particularly in the p-type GaAs layer 3 having thin film thickness of 0.5 .mu.m, open voltage V.sub.OC, curve factor FF and short-circuit current I.sub.SC, which are correlated with photoelectric conversion efficiency, are reduced by thermal or mechanical stress for bonding. Consequently, reduction is caused in photoelectric conversion efficiency and reliability of the device.